Gypsum products and method for their manufacture

ABSTRACT

A method is provided which uses an improved emulsion to imparting water-resistance to gypsum products. In one embodiment, gypsum products comprise calcium sulfate dihydrate and an emulsion which comprises a saponified wax, a nonsaponifiable wax, an alkyl phenol, a surfactant/dispersant salt of polynaphthalenesulfonic acid, and carboxymethylcellulose. Optionally, the emulsions may contain a preservative, e.g., a biocide (mildewcide, fungicide, etc.). These gypsum products resist the uptake of water and therefore resist biological infestation without addition of a preservative.

The present invention relates to a wax emulsion additive useful inimproving the water-resistance of gypsum products such as gypsum boardand gypsum wood fiber products. The present invention further relates toa method of making the gypsum products using emulsion additives.

Certain properties of gypsum (calcium sulfate dihydrate) make it verypopular for use in making industrial and building products, especiallygypsum-containing panels. Gypsum is a plentiful and generallyinexpensive raw material which, through a process of dehydration andrehydration, can be cast, molded or otherwise formed to useful shapes.The base material from which gypsum board is manufactured is thehemihydrate form of calcium sulfate (gypsum), commonly termed stucco,which is produced by the heat conversion of the dihydrate from which thewater phase has been removed. The gypsum products in the panel boardindustry, include, but are not limited to, paper backed gypsum board,specialty gypsum board reinforced with glass mats and, as describedfurther below, gypsum wood fiber products incorporating wood or ligninfibers, and other products.

A gypsum wood fiber (GWF) product differs from conventional gypsumwallboard products in that the GWF incorporates into the establishedslurry both gypsum and lignocellulosic material, e.g., wood fibers. Theamount of wood fiber or other lignocellulosic material may be about 50wt. % to about 95 wt. %, based on the combined weight of the gypsum andlignocellulosic material. A typical GWF product may comprise about 80%wood fiber by weight, based on the combined weight of gypsum and woodfiber. The lignocellulosic material is commonly referred to in the artas wood furnish. Sources of wood furnish include, but are not limitedto, softwood such as pines, spruces and firs, and hardwood such as oaks,maples, eucalyptuses, poplars, beeches, and aspens. These products, likeordinary gypsum wallboard, gypsum tile, gypsum block, gypsum casts, andthe like have relatively little resistance to water.

Gypsum products absorb water, which reduces their strength. Prior artproducts, like ordinary gypsum board, gypsum tile, gypsum block, gypsumcasts, and the like have relatively little resistance to water. Actualtests have demonstrated that when a 2 inch by 4 inch cylinder of gypsumboard core material was immersed in water at about 70° F., the cylindershowed a water absorption of 36% after immersion for 40 minutes. Whenordinary gypsum board is immersed in water, the board quickly absorbs aconsiderable amount of water, and loses a great deal of its strength. Ineach of the gypsum products mentioned above, therefore, it is desirableto control the water uptake or absorption. Water also makes gypsumproducts susceptible to the growth of mold, mildew, fungi and otherbiological agents.

Historically, products added to a gypsum slurry to impart a degree ofwater-resistance in the board manufacturing process have incorporatedasphalt, molten wax, emulsified wax/asphalt, emulsified wax, and varioussilicone products. These prior art systems have all demonstratedshortfalls in any number of performance related areas. These shortfallsinclude, but are not limited to, inconsistent solids, instability of theemulsions, wide ranges in apparent viscosity, a caustic pH requiringhazardous labeling, health risks due to the evolution of hydrogen andhydrogen sulfide gases. An additive is needed that can address theaforementioned issues and impart water-resistance to a gypsum product.

U.S. Pat. No. 6,663,707 to Wantling et al, dated Dec. 16, 2003(published Jul. 17, 2003), teaches the incorporation of a generic starchspecies from corn, sago, wheat, rice, etc., with a complexing agent suchas sodium borate in combination with other chemical compounds,specifically sodium lignosulfate, and C24 and greater polymerized alkylphenol and various waxes forms a nearly stable wax emulsion suitable forincorporation into a gypsum slurry to impart water-resistance. Whilethis system shows significant advantages over previously available waxemulsions it to suffers from a number of deficiencies, including:degradation of the pH due to bacteriological activity resulting from thedecomposition of the sodium lignosulfate in long-term storage, viscositychanges as temperature and age occur manifesting itself as a slightseparation at the water/wax interface, and less than predictable userates at the mixer due to the changes occurring singularly and incombination.

U.S. Pat. No. 6,010,596 to Song teaches adding a wax emulsion containinga combination of a paraffinic hydrocarbon, montan wax, polyvinylalcohol, water and emulsifiers to a hot slurry containing ground gypsumand wood fiber. Emulsifiers include nonionic and cationic surfactants.While still hot, the slurry is discharged through a headbox onto acontinuous felting conveyor, such as the type used in paper makingoperations, to form a filter cake and remove as much uncombined water aspossible.

Accordingly, there is a need for an additive which is useful inimparting water-resistance to gypsum products, and which is economicalto apply. There is a need for a water-resistance additive which does notrequire the use of costly components such as polysiloxane. There is afurther need for a water-resistance additive which is stable at roomtemperature and which does not require heating prior to application to agypsum solution. There is still a further need for a stablewater-resistance additive which does not require continuous mixing oragitation to maintain its stability. Accordingly, there is a need amethod for making gypsum products that addresses one or more issues ofwater absorption, viscosity control, stability, and slurry fluidity whenused to make gypsum products. Of course, such an additive should performthese functions without affecting fluidity, foamability, pre-set time orset time.

SUMMARY OF THE INVENTION

Disclosed herein is a method for making a gypsum product comprisesforming a slurry comprising gypsum, water and an emulsion comprising anonsaponifiable wax, a saponified wax, an alkyl phenol component, adispersant/surfactant, a carboxymethylcellulose component, and water. Ina particular embodiment, the nonsaponifiable wax may comprise about 33%to about 35% of the emulsion, by weight, the saponified wax may compriseabout 3% to about 5% of the emulsion, by weight, the alkyl phenolcomponent may comprise about 0.5% to about 2.5% of the emulsion, byweight, the dispersant may comprise about 0.5% to about 2% of theemulsion, by weight, and the carboxymethylcellulose component maycomprise about 0.2% to about 5% of the emulsion, by weight. Optionally,the emulsions may comprise a preservative, e.g., a biocide (rmildewcide,fingicide, etc.). In various embodiments, the gypsum product maycomprise gypsum board or a gypsum wood fiber product. Also describedherein are gypsum products comprising gypsum, a wax component comprisinga nonsaponifiable wax and a saponified wax, an alkyl phenol component, adispersant/surfactant, and a carboxymethylcellulose component.

The above described and other features are exemplified by the followingdetailed description.

DETAILED DESCRIPTION

The manufacture of gypsum products, including gypsum board andcomposites made using gypsum, such as gypsum fiber composites, glassfiber-filled gypsum products, gypsum wood fiber products, etc.(collectively referred to as ‘gypsum products’), may employ emulsionsdescribed herein to provide water resistance (hydrophobicity) to suchproducts. When these emulsions are used, the maximum water absorptionrealized by such products is reduced as compared to products for whichsuch emulsions are not used, i.e., the emulsions improve the waterresistance characteristic of the products. By improving the waterresistance of gypsum products, these emulsions ameliorate thedetrimental effects that absorbed water can have on such products,including causing dimensional instability (swelling), loss of mechanicalstrength and biological degradation. The emulsions may also serve ascarriers for optional additives such as fire retardants andpreservatives which are not themselves water-repellant.

The manufacture of gypsum products generally comprises preparing agypsum-containing slurry that contains gypsum and other components ofthe finished product, and then processing the slurry to remove the waterand form and dry the remaining solids into the desired form. In themaking of gypsum board, the gypsum is rendered into a slurry which mustflow onto a paper substrate. The slurry/substrate combination is thensized in a continuous process by passing this combination betweenrollers. Simultaneous with this sizing step, a paper backing ispositioned over the sized gypsum slurry. Accordingly, the gypsum slurrymust possess sufficient fluidity so that a properly sized gypsum boardcan be made. Fluidity refers to the ability of the gypsum slurry toflow.

It is also important to the manufacture of gypsum board that the gypsumslurry be capable of being foamed to a limited extent. Foamabilityrefers to this ability to be foamed. When the gypsum slurry and papersubstrate are passed through the sizing rollers, a certain amount of thegypsum slurry must back flow and accumulate in the rollers nip so that asteady flow of gypsum is delivered to the sizing rollers. Foamability isimportant to this ability of the gypsum slurry to back flow at therollers nip. Forming plates may be used, eliminating the use of a masterroll, but foam is important to control density of the finished product.

The manufacture of gypsum board is a continuous manufacturing processwherein the gypsum slurry flows onto a substrate which then passesthrough sizing rollers. Therefore, the extent to which the gypsum slurryflows after it is sized is critical to maintaining the finished productdimensions of the gypsum board. The time interval from when the slurryis sized to when the gypsum slurry ceases its flow is referred to as thepre-set time. Therefore, pre-set time is an important property of thegypsum slurry. The set time of the gypsum slurry is also an importantproperty. The set time refers to the amount of time it takes the gypsumslurry to be dried, under heat, to the finished, solid gypsum board. Asis well known in the art, in a continuous gypsum board manufacturingprocess, it is important that the gypsum slurry possess a consistent settime.

Unlike the production of gypsum board, the production of a GWF productis facilitated through a conventional paper making process. The processof water felting dilute aqueous dispersions of various fibrous materialsis a well-known commercial process for manufacturing many types of paperand board products. In this process, an aqueous dispersion of fiber,binder and other ingredients, as desired or necessary, is flowed onto amoving foraminous support wire, such as that of a Fourdrinier or Olivermat forming machine, for dewatering. The dispersion may be firstdewatered by gravity and then dewatered by vacuum suction means; the wetmat is then pressed to a specified thickness between rolls and thesupport wire to remove additional water. The pressed mat is then driedin heated convection or forced air drying ovens, and the dried materialis cut to the desired dimensions. The manufacture of gypsum wood fiberproducts may be carried out similarly, utilizing a wet end sectionheadbox distribution mechanism distributing the gypsum wood fiber slurryonto a vacuum wire for initial mat formation and dehydration followed bycompression through a series of vacuum belt rolls and into a kiln forfinal dehydration. The addition of the emulsion does not cause waxplating or break-out on the vacuum belt. The gypsum wood fiber of thepresent invention does not incorporate paper face and back paper butrather is a paperless core that has similar performance and usescomparable to conventional sheathing products currently available.

An emulsion as described herein is used in the manufacture of a gypsumproduct (gypsum board, gypsum wood fiber products, etc.) byincorporating the emulsion into the gypsum-containing slurry that isused to make the gypsum product. Such an emulsion may comprise a waxcomponent comprising a nonsaponifiable wax and a saponified wax (whichmay be formed during the preparation of the emulsion by the reaction ofa saponifiable wax and a saponifier), an alkyl phenol component, adispersant/surfactant, a carboxymethylcellulose component, and water. Incontrast to the emulsion described in U.S. Pat. No. 6,663,707, theseemulsions are optionally free of starch such as a complexed starch,and/or free of co-surfactants such as calcium lignosulfonate, sodiumlignosulfonate and/or trisodium phosphate. The emulsion typically isadded in an amount designed to provide about 1.5 weight % (wt. %) toabout 3 wt. % wax in the finished product. The processing of the slurryis believed to break the emulsion, which releases the waxes therein andallows the waxes to migrate to the surface of the product, thusenhancing the water-resistance characteristics. Since water is aprincipal contributor to biological activity, the use of these emulsionsreduces and may, in some cases, eliminate, biological activity in thegypsum product, without the need for a biocide. Optionally, however, theemulsions described herein can be adjuvants for impregnatingpreservatives into gypsum products in amounts effective to inhibit abiological activity, i.e., biological degradation, such as the growth ofmildew, molds, fungi, etc.

Emulsions described herein comprise a wax component comprising anonsaponifiable wax and a saponifiable wax. The nonsaponifiable wax maycomprise a wax having a melting point greater than about 120° F. (about49° C.), e.g., about 120° F. to about 165° F. (about 49° C. to about 74°C.), optionally about 120° F., to about 150° F. (about 49° C. to about66° C.), and preferably about 135° F. to about 145° F. (about 57° C. toabout 63° C.). (All ranges disclosed herein are inclusive andcombinable, e.g., the ranges of “about 120° to about 165° F., optionallyfrom 135° to 145° F.”, are inclusive of the endpoints and allintermediate values of the ranges and combinations thereof, including,e.g., about 120° to about 145° F., about 130° to about 150° F., etc.)Suitable nonsaponifiable waxes include paraffin waxes, slack waxes andscale waxes. Such waxes are commercially known to be of low volatility,exhibiting less than about a 10% loss in weight during standardthermogravimetric analysis. Also, the oil content of these waxes istypically less than about 5% by weight, preferably less than about 1% byweight. Some of these waxes are of a relatively high molecular weight,having an average chain length of C₃₆, that is a 36 carbon chain length,or greater. Paraffin waxes are typically derived from light lubricatingoil distillates and are predominantly straight chain hydrocarbons havingan average chain length of 20 to 30 carbon atoms. Suitable paraffinwaxes include Wax 3816 available from Honeywell/Astor of Duluth, Ga.Slack waxes are petroleum waxes having an oil content of 3 wt. % to 50wt. %. Suitable slack waxes include Exxon 600 Slack Wax and Ashland 200Slack Wax, and a combination of 50 parts Exxon 600 Slack Wax and 50parts Ashland 200 Slack Wax.

A suitable saponifiable wax has an acid value or a saponification valueand a melting point greater than about 180° F. (about 82° C.).Saponifiable waxes include waxes from the liquefication of coal,vegetable waxes and oxidized waxes resulting from the processing and/orrefining of slack wax, scale wax or crude petroleum. For example,saponifiable waxes include montan wax, carnauba wax, beeswax,bayberry-myrtle wax, candelilla wax, caranday wax, castor bean wax,esparto grass wax, Japan wax, ouricury wax, retamo-ceri mimbi wax,shellac, spermaceti wax, sugar cane wax, wool-lanolin wax, and others.One example of a useful saponifiable wax is a montan wax having a meltpoint of about 190° to about 200° F. (about 88° to about 93° C.) meltpoint. Saponification of such waxes occurs as a result of combining thewax with a saponifier, i.e., strongly basic material such as ammoniumhydroxide or an alkali metal hydroxide such as sodium hydroxide orpotassium hydroxide. The amount of saponifier needed to saponify a waxmay be calculated based on the saponification value of the wax. Forexample, the saponification value divided by 1000 equals the grams ofpotassium hydroxide to add per gram of wax.

Preferably, the waxes do not contain more than about 5% (by weight)polar compounds as impurities.

The wax component may be present in an amount of about 25 percent byweight (wt. %) to about 50 wt. %, based on the total weight of theemulsion, preferably about 30 wt. % to about 40 wt. %. Preferably, thewax component comprises a combination of a nonsaponifiable wax having amelting point of greater than or equal to about 120° F. and asaponifiable wax. The nonsaponifiable wax may comprise about 25 wt. % toabout 44 wt. % of the total weight of the emulsion, and the saponifiablewax may comprise about 0.5 wt. % to about 5 wt. % of the total weight ofthe emulsion. A preferred combination of waxes is a combination of aparaffin wax such as Honeywell 3816 as the first wax and a saponifiablewax such as montan wax. In one embodiment, the wax component comprisesparaffin wax in an amount of about 25 wt. % to about 45 wt. %,preferably about 30 wt. % to about 40 wt. %, and saponifiable wax in anamount of about 2.5 wt. % to about 5 wt. %, preferably about 3.5 wt. %to about 4.5 wt. %, based on the total weight of the emulsion.

A strongly basic compound is added to the emulsion mixture to saponifythe saponifiable wax. The saponifier may comprise, e.g., ammoniumhydroxide or an alkali metal hydroxide, e.g., sodium hydroxide orpotassium hydroxide. The alkali metal hydroxide may be provided in theform of a concentrated aqueous solution that may comprise about 45%alkali metal hydroxide, by weight. Ammonium hydroxide may be provided insolid form. Some or all of the saponifier may also react with thedispersant, and/or with other component ingredients of the emulsion, insitu. Although ammonium hydroxide is sometimes objected to because ofthe ammonia odor it produces, ammonium hydroxide is believed to beadvantageous because, in addition to saponifying the wax, the ammoniacan serve as a scavenger for formaldehyde in the resin with which theemulsion is used, and may thus reduce the emission of formaldehyde fromthe finished composite product. The combination of ammonium hydroxidewith formaldehyde also ameliorates the ammonium hydroxide odor, so insome embodiments, formaldehyde may be added to the emulsion for thispurpose, for example, in an amount of about 0.02 to about 0.1% byweight. In addition, ammonium hydroxide is especially advantageous forwhen the emulsion is used with lignocellulosic materials comprisingnorthern wood species, i.e., Douglas fir, aspen and the like.

The saponifier may be provided in an amount of about 0.15% to about4.5%, optionally about 0.5% to about 3%, of the emulsion, by weight.Optionally, concentrated aqueous saponifier may be provided in an amountof about 0.5 to about 3% by weight of the emulsion; ammonium hydroxidemay be added in solid form in an amount of about 0.15 to about 3% byweight of the emulsion. The amount of saponifier may be varied with thetype of saponifiable wax used, or with the type of wood. As a result ofthe saponifier, an emulsion as described herein may have a pH of about8.5 to about 12.5, for example, a pH of about 8.5 to about 9.5.

Exemplary carboxymethylcellulose materials useful in these emulsionshave molecular carbon chain lengths of about 20 to about 50 carbons. Anexample of a suitable carboxymethylcellulose is carboxymethylcellulosesodium, available from Penn Carbose, Somerset, Pa., under the tradedesignation LT-30, which is described as having carbon chain lengths ofabout 26 to 30 carbons. Other suitable carboxymethylcellulose materialsinclude Penn Carbose LT-20 and LT-42. The carboxymethylcellulose and theproduct of its reaction with the saponifier or with any other componentin the emulsion are referred to herein as the “carboxymethylcellulosecomponent”.

A salt of polynaphthalenesulfonic acid is useful in the emulsionsdescribed herein and, without wishing to be bound by theory, is believedto act as a dispersant/surfactant. The salt may be the product of anin-situ reaction of polynaphthalenesulfonic acid and a saponifier, e.g.,an alkali metal hydroxide. One commercially availablepolynaphthalenesulfonic acid is DISAL GPS which may be obtained fromHandy Chemical, Montreal, Quebec, Canada. The acid and acid salt arereferred to collectively as a polynaphthalenesulfonic acid component or,more broadly (to include substitute materials), as thedispersant/surfactant. The dispersant/surfactant may comprise about 0.1%to about 5% of the emulsion, by weight, optionally about 0.25 wt. % toabout 5 wt. %.

Incorporating an alkyl phenol into the emulsions has been found tofacilitate achieving low water absorption in the final lignocellulosiccomposite product. As used herein, “alkyl phenol” refers to a phenoliccompound having a long chain alkyl group. The long chain alkyl group maybe straight or branched. The long chain alkyl group may be C₂₀-C₄₂ (from20 to 42 carbon chain length), e.g., C₂₄-C₃₄, preferably C₂₄-C₂₈. Suchalkyl phenols include polymerized methylene-coupled alkyl phenol,phenate salts, calcium phenates, long branched chain calcium alkylphenols, long straight chain calcium alkyl phenols and complex polymersof maleic acid with and without an amine group substitution. The longchain alkyl group may be a polymeric group such as a polyethylene,polypropylene, or polybutylene group, for example. The alkylsubstituents may be a mixture of different chain lengths as is often thecase with commercially available materials. Preferably, the alkyl phenolis chosen so that the average carbon chain length of the alkyl portionmatches, i.e., is approximately the same as or is close to, the averagecarbon chain length of the carboxymethylcellulose. For example, an alkylphenol of average chain length in the range of about C₂₄ to about C₃₄may be used in an emulsion comprising carboxymethylcellulose having anaverage chain length of about 26 to about 32 carbons, e.g., CarboseLT-30 carboxymethylcellulose.

The alkyl group of the alkyl phenol can be derived from a correspondingolefin; for example, a C₂₆ alkyl group is derived from a C₂₆ alkene,preferably a 1-alkene, a C₃₄ alkyl group is derived from a C₃₄ alkene,and mixed length groups are derived from the corresponding mixture ofolefins. When the alkyl group is an alkyl group having at least about 30carbon atoms, however, it may be an aliphatic group (or a mixture ofsuch groups) made from homo- or interpolymers (e.g., copolymers,terpolymers) of mono- and di-olefins having 2 to 10 carbon atoms, suchas ethylene, propylene, butene-1, isobutene, butadiene, isoprene,1-hexene, and 1-octene. Aliphatic hydrocarbyl groups can also be derivedfrom halogenated (e.g., chlorinated or brominated) analogs of such homo-or interpolymers. Such groups can, however, be derived from othersources, such as monomeric high molecular weight alkenes (e.g.,1-tetracontene) and chlorinated analogs and hydrochlorinated analogsthereof, aliphatic petroleum fractions, particularly paraffin waxes andcracked and chlorinated analogs and hydrochlorinated analogs thereof,white oils, synthetic alkenes such as those produced by theZiegler-Natta process (e.g., poly(ethylene) greases) and other sourcesknown to those skilled in the art. Unsaturation in the hydrocarbylgroups can be reduced or eliminated, if desired, by hydrogenationaccording to procedures known in the art. Preparation by methods andmaterials that are substantially free from chlorine or other halogens issometimes preferred for environmental reasons.

More than one alkyl group can be present, but usually no more than 2 or3 are present for each aromatic nucleus in the aromatic group. Mosttypically only one hydrocarbyl group is present per aromatic moiety,particularly where the hydrocarbyl-substituted phenol is based on asingle benzene ring.

The alkyl phenol and product of the reaction of an alkyl phenol with asaponifier or with any other component of the emulsion is referred toherein as the alkyl phenol component.

The amount of alkyl phenol component present in the emulsion is about0.25 wt. % to about 10 wt. %, optionally about 0.5 wt. % to about 2.5wt. % based on the total weight of the emulsion.

One example of an alkyl phenol component useful in the compositions ofthe present invention is commercially available under the tradedesignation 319H from Lubrizol Chem. Corp. Wycliffe, Ohio, whichmaterial is described as a C₂₄-C₃₄ polymerized methylene-coupled alkylphenol. Various other, commercially available alkyl phenols that may beused in these emulsions, include the following (identified by arbitraryidentifier numbers in the following Table 1:

TABLE 1 Identi- fication No. Description Source 319A Complex polymer ofmaleic acid “Flozol 140” (no amine group substitution) Lubrizol Chem.Corp. Wycliffe, Ohio 319B Complex polymer of maleic acid “Flozol 145”(with amine group substitution) Lubrizol Chem. Corp. Wycliffe, Ohio 319CStraight chain, long chain alkyl Lubrizol Chem. Corp. phenol Wycliffe,Ohio 319D Calcium Phenate Lubrizol Chem. Corp. Wycliffe, Ohio 319EBranched chain, long chain alkyl Lubrizol Chem. Corp. phenol Wycliffe,Ohio 319H C 24-C 34 polymerized methylene- Lubrizol Chem. Corp. coupledalkyl phenol Wycliffe, Ohio

One method of manufacture for the emulsions described herein results intime, energy, operator, and production efficiencies. The method involvesmixing the ingredients of the emulsion in a single vessel and thenconveying the mixture of a homogenizer under conditions such as thefollowing. An advantage of this method is that the emulsion mixture isprepared in a single vessel; it is not necessary to prepare andseparately store partial mixtures of the ingredients of the emulsion inseparate vessels before combining them together.

In one embodiment of a ‘single vessel’ method, the nonsaponifiable wax(e.g., 3816 wax, further described below) is melted and stored in moltenform, e.g., at about 10° F. above its melt point temperature, and wateris provided at a temperature that will not cause the wax to solidify.The vessel is then charged in the following illustrative manner:

-   -   a. Charge the melted nonsaponifiable wax, e.g., 3816 wax, at a        temperature of about 189° F. to about 192° F. (about 87° C. to        about 89° C.);    -   b. Start heat and agitation;    -   c. Charge molten saponifiable wax and alkyl phenol with        continued agitation;    -   d. Charge a majority of the water, e.g., 95%, and continue        agitation;    -   e. Charge the dispersant/surfactant, (e.g., DISAL        polynaphthalenesulfonic acid, further described elsewhere        herein), carboxymethylcellulose and saponifier;    -   f. Charge the remaining water—preferably including the water        used to rinse the tubes calculated and subtracted out of the        total;    -   g. Bring the tank up to temperature, e.g., about 190° F. to        about 210° F. (about 88° C. to about 100° C.);    -   h. Continue to agitate while maintaining temperature for about        30 to about 150 minutes;    -   i. Put through homogenizer at about 1500 to about 3500 PSI        (about 10 megaPascals (MPa) to about 24 MPa);    -   j. Cool, optionally in process that provides two exotherms,        including a first exotherm between the exit temperature from the        homogenizer to a temperature above ambient, and a second exothem        to ambient (storage) temperature. For example, the emulsion        composition is passed from the homogenizer to a cooler to        achieve a first exotherm of, e.g., about 10° F. to about 20° F.        degrees lower than the homogenizer exit temperature, and then to        a cooling tank to achieve a second exotherm of, e.g., about an        additional 5° F. to about 15° F. lower, optionally under        agitation. In one embodiment, the first exotherm may occur by        cooling from about 130° F. to about 110° F., and the second        exotherm may occur by cooling from about 110° F. to about 70° F.

Without wishing to be bound by any particular theory, using atwo-exotherm cooling process allows a phasing process of the formationof the emulsion to proceed to completion. As a result, the viscosity ofthe emulsion is more stable over time and the emulsion is more stablewhen subject to shear agitation than if a single exotherm coolingprocess is used. In an alternative method of preparing the emulsion, abatch process may be used in which a first premix comprising the moltenwaxes and alkylphenol may be prepared, and a second premix (an aqueouspremix) comprising the water, carboxymethylcellulose andpolynaphthalenesulfonic acid and saponifier may be prepared, and thefirst and second premixes may then be combined in a mixing tank for atime sufficient at least for the waxes to become saponified, e.g., forone to three hours, and the resulting mix may then be passed to ahomogenizer and cooled as described above.

Illustrative ranges of ingredients in some embodiments of emulsionsdescribed herein are provided in Table 2 below.

TABLE 2 ILLUSTRATIVE EMBODIMENTS Component Typical Amount (% weightbasis) Nonsaponifiable Wax 33-35 Saponifiable Wax 3-5 Alkyl Phenol0.5-2.5 Polynaphthalenesulfonic Acid 0.5-2   Carboxymethylcellulose0.2-5   Saponifier Amount used depends on amount of saponifiable wax;typically 0.5-3 Water Balance (to 100)

The following Table 3 provides example proportions of ingredients in aspecific embodiment of an emulsion as described herein.

TABLE 3 ILLUSTRATIVE EMULSION INCLUDING POLYNAPHTHALENESULFONIC ACIDComponent Weight % Wax 3816 33.00 Saponifiable Wax 3.00 Alkyl Phenol0.50 Polynaphthalenesulfonic Acid 0.50 (DISAL GPS)Carboxymethylcellulose 0.2 45% KOH (saponifier) 0.75 Water Balance (to100)

An emulsion as described herein may have a viscosity of about 10 toabout 100 centipoise, measured on a Brookfield viscometer. One sampleemulsion had a viscosity of 9 cps at about 40% solids. The stability andshear performance and lack of foam generation further enhance theability to receive these emulsions. For example, one sample emulsionremained intact even after four minutes agitation in a food blender.Embodiments of these emulsions have been demonstrated not to contributeto biological activity.

A series of sample emulsions was made with the following commoningredients: 33% nonsaponifiable wax; 3% montan wax, 0.5% alkylphenol;2% polynaphthalenesulfonic acid (or, where noted 2.5%); 0.5%carboxymethylcellulose. The various emulsions were made with thequantity of saponifier, the nonsaponifiable waxes and with additionalcomponents in the amount set forth in the following Table 4, with watercomprising the balance. The samples of Table 4 were prepared using thebatch process described above. In emulsions B and E, the indicatedformaldehyde was included in the aqueous premix; in emulsions C, F, G,H, and I, the indicated formaldehyde was added to the emulsion after theemulsion was formed from the other components.

TABLE 4 Ammonium Nonsaponifiable Emulsion hydroxide formaldehyde wax A0.38% 0.0 3816 B 0.38% 0.25 3816 C 0.38% 0.25 3816 D 0.45% 0.0 3816 E0.45% 0.25 3816 F 0.45% 0.25 3816 G^(i) 0.45% 0.25 3816 H 0.45% 0.25Prowax^(ii) 561 I 0.45% 0.25 Prowax^(ii) 321 J 0.45% 0.0 3816^(i)Emulsion G contained 2.5% polynaphthalenesulfonic acid ^(ii)Prowax561 and 321 are hard paraffin waxes commercially available fromExxonMobil Corporation

The utility of emulsions described herein in gypsum board wasdemonstrated as follows.

Test specimen slurries were made by mixing 50 grams of gypsum, 35.97grams of water, and 1.92 grams of an emulsion set forth in Table 4. In acontrol slurry, no emulsion was added. Gypsum and water and, if added,emulsion, were mixed together and left to stand for one minute. Thismixture was then mixed for an additional 30 seconds. After this secondmixing, the specimen slurries were subjected to fluidity testing.

The specimen slurries were poured out onto a flat surface and thediameter of the resulting patty (“slump size”) was measured. Thediameter of a patty is an index of the fluidity of the specimen. Thelarger the diameter, the more fluid the specimen. The results are setforth in the following Table 5, in which the specimen slurries areidentified according to the emulsion they contained.

The foamability test is used to determine the affect of a wax emulsionon the stability of foam in a gypsum slurry. In this test, 0.60 grams ofa commercially available foamant and 2 grams of wax emulsion are weighedout. The foamant and the emulsion are placed into a blender along with100 grams of water, and the mixture is blended for 20 seconds. At theend of this blending step, the foam is immediately poured from theblender cup into a tared 150 ml beaker to overflowing. Any excess isstruck off the beaker. Any foam remaining in the blender cup is setaside. The foam density is determined by weighing the foam in the 150 mlbeaker. Two minutes after the blending has stopped, any liquid in theremaining foam in the blender cup is drained and discarded. A clean,tared, 150 ml beaker is filled with the remaining foam to overflowingand the excess is struck off. A second foam density is determined asjust described. The slurries containing emulsions of Table 4 yieldedfoam densities that were acceptable (i.e., compared favorably to thecontrol) and ranged from about 40 to about 65 grams per 150 ml, for themeasurements made at 20 seconds, and from about 10 to about 45 grams per150 ml, for the measurements made at 2 minutes.

The patties made in the Fluidity Test were dried for at least 24 hoursat 110° F. (43.3° C.). At the end of this time, the patties were weighedand the weight was recorded. The dried patties were then immersed inwater for two hours. At the end of the two-hour immersion, the pattieswere weighed and this wet weight was recorded. Percent water retentionwas then calculated based on the difference between these two recordedweights. The results are set forth in the following Table 5, in whichthe specimen slurries are identified according to the emulsion theycontained.

TABLE 5 Dry Wet Slurry Weight Weight Identification Slump Size (grams)(grams) % Abs. Blank  10.3 cm 50.41 68.07 35 (4 1/16″) A  9.7 cm 49.8650.06 0.41 (3 13/16″) A  9.7 cm 50.23 50.42 0.38 (3 13/16″) B   10 cm50.6 50.76 0.32 (3 15/16″) B 10.16 cm 50.41 50.36 −0.09 (4″) C  10.6 cm42.49 52.44 0.3 (4 3/16″) C  10.8 cm 52.77 52.84 0.13 (4¼″) G  10.8 cm53.81 53.71 −0.18 (4¼″) G 10.95 cm 53.24 53.14 −0.19 (4 5/16″) H  9.2 cm46.84 47.99 2.46 (3⅝″) H  9.2 cm 47.56 48.19 1.32 (3⅝″) D 10.16 cm 50.9151.26 0.69 (4″) D 10.16 cm 51.08 51.12 0.08 (4″) E 10.16 cm 50.93 510.14 (4″) E 10.16 cm 49.81 50.14 0.66 (4″) F 10.16 cm 51.89 52.18 0.56(4″) F  10.3 cm 51.89 51.78 −0.21 (4 1/16″) G  10.3 cm 54.94 5482 −0.22(4 1/16″) G  11.4 cm 54.72 54.61 −0.2 (4½″)

As can be seen from the data of Table 5, the specimen slurries allexhibited fluidity comparable to the control; all were adequately fluid.In addition, the amount of water absorption for gypsum products madewith wax emulsions was very significantly reduced from the 35% waterabsorption of the control gypsum product that made without the waxemulsions.

One embodiment of a method for making a gypsum wood fiber productcomprises:

-   -   (a) mixing a slurry containing about 95 parts to about 50 parts        of a wood fiber (by weight), about 5 parts to about 50 parts of        gypsum, about 1 part to about 3 parts emulsion, balance water;    -   (b) distributing the slurry onto a vacuum wire for formation of        a mat;    -   (c) partially drying the mat of step (b);    -   (d) compressing the mat of step (c) through a series of vacuum        belt rolls; and    -   (e) drying the compressed mat of step (d) in an oven.

The amount of water in the slurry is an amount sufficient to facilitatedepositing the slurry onto a vacuum wire for the formation of a mat.Various gypsum wood fiber articles may be made by this method including,but not limited to, wallboard and sheathing.

These wax-in-water emulsions may be added to a gypsum slurry withoutadversely affecting properties of the slurry which are necessary to themanufacture of gypsum products, i.e., fluidity, foamability, set time,etc. In optional embodiments, a dispersing aid, or fluidity modifier, isuseful for the maintenance of the fluidity of the gypsum/emulsionmixture. Such dispersing agents are strong lipophiles, which are,consequently, good defoamers. One such dispersing agent ispoly(oxy-1,2-ethanedyl), alphaphenyl-omega-hydroxy styrenate.

The use of the emulsions described herein provides significantlyimproved performance in both water uptake and edge and center swell invarious gypsum products, allows relaxed storage requirements of thefinished gypsum product, adds less wax and other emulsion components tothe gypsum product than other emulsions at comparable water resistancerates for which the finished products must contain about 5 wt. % toabout 6 wt. % wax. Not only does this lead to the use of less material,it also yields a gypsum product that emits fewer volatile emissions thangypsum products containing more wax. Further, these emulsions areamphoteric and will therefore be stable under a wide range of pH.

One or more preservatives, e.g., bactericides/fungicides, mildewcides,or other biocides, may optionally be included in a gypsum product byincorporating the preservative into the emulsion or into thegypsum-containing slurry. One example of a preservative suitable forgypsum products is a bactericide/fungicide known commercially as METASOLD3TA, which comprises 3,5-dimethyl-tetrahydro-1,3,5,2 Hthiadiazine-2-thione. METASOL D3TA may be obtained from Ondo-Nalco,Houston, Tex. Mildewcide can include any commercially availablemildewcide including formaldehyde. Other suitable biocides includebis-thio-benzene, propiconazole and bis(tributyltin)oxide. Optionally,one or more of these biocides or the others mentioned below may beincorporated into the gypsum-containing slurry in an amount calculatedto be about 0.0025% to about 0.2% by weight of the product, optionallyin the emulsion in an amount of about 0.1% to about 2% by weight of theemulsion.

To evaluate the ability of emulsions described herein to help retainabsorbed preservatives (mildewcides, fungicides, etc.) for resistance tothe growth of mold in gypsum products, a series of gypsum products wereprepared and tested in accordance with the procedure described in ASTM D3273. Separate gypsum panels were prepared using emulsions constitutedto replicate emulsion G (Table 4), emulsions differing from emulsion Gby the use of 0.1% formaldehyde rather than 2.5%, and emulsionsdiffering from emulsion G by the absence of formaldehyde. In addition,gypsum panels were made with various samples of these emulsions thatalso included propiconazole, bis(tributyltin)oxide, or METASOL D3TA, inamounts of 0.2 wt %, 0.5 wt %, 0.75 wt % and 1 wt %. Briefly restated,the test described in ATSM D32-73 involves preparing a test chamber thatincludes a tank measuring about 46 centimenters (cm) by 46 cm by 61 cminto which water is added to a depth of about 50 to 75 millimeters. Thechamber is held at a relative humidity of 95 to 98% at a temperature of32.5° C. The chamber is further prepared for the test by placing a trayof greenhouse-grade potting soil in the chamber above the water, andinoculating the soil with cultures of Aureobasidium pullulans,Aspergillus niger and Penicillium. The mold is allowed to sporulate andequilibrate with the chamber for about two weeks. Test panels may thenbe hung in the chamber with the bottom about 75 millimeters above theinoculated soil. Mold growth on the surface of the panels is notedweekly for four weeks. Under such a test, if a panel supports moldgrowth, moderate mold growth is evident within 2 to 3 weeks. After theinitial two weeks of the test period, none of the samples show signs ofmold growth. This indicates that the water resistance imparted by theemulsions described herein leads to a significant inhibition of mold andother biological growth. It is expected that the samples containingbiocide preservatives will resist biological growth for a longer periodthan those that do not contain biocide preservatives.

Suitable preservatives that may be incorporated into gypsum productswith an emulsion described herein may be inorganic or organic, andinclude, for example biocides such as mildewcides and, fungicides andcombinations thereof. The biocide may be chosen according to (1) thetarget organism; (2) solubility characteristics; (3) stability to thetemperature and pH; and other conditions found in the manufacture of thegypsum product. Biocides include substances that kill or inhibit thegrowth of microorganisms such as molds, mildew, slimes, fungi, bacteria,etc. Fungicides include substances that kill or inhibit the growth offungi. More specific examples of biocides include, but are not limitedto, chlorinated hydrocarbons, organometallics, halogen-releasingcompounds, metallic salts, organic sulfur compounds, and phenolics.

Suitable fungicides include, for example, zinc dimethyl dithiocarbamate,2-methyl-4-t-butylamino-6-cyclopropylamino-s-triazine,2,4,5,6-tetrachloroisophthalonitrile, N,N-dimethyl dichlorophenyl urea,copper thiocyanate, N-(fluorodichloromethylthio)phthalimide,N,N-dimethyl-N′-phenyl-N-′fluorodichloromethylthiosulfamide; copper,sodium and zinc salts of 2-pyridinethiol-1-oxide; tetramethylthiuramdisulfide, 2,4,6-trichlorophenyl-maleimide,2,3,5,6-tetrachloro-4-(methylsulfonyl)-pyridine, diiodomethyl p-tolylsulfone, phenyl (bispyridil)bismuth dichloride,2-(4-thiazolyl)-benzimidazole, pyridine triphenyl borane, phenylamides,halopropargyl compounds, propiconazole, cyproconazole, tebuconazole and2-haloalkoxyaryl-3-isothiazolones (such as2-(4-trifluoro-methoxyphenyl)-3-isothiazolone,2-(4-trifluoromethoxy-phenyl)-5-chloro-3-isothiazolone,2-(4-trifluoromethoxyphenyl)-4,5-dichloro-3-isothiazolone), andcombinations comprising one or more of the foregoing fungicides.

The fungicide may be an agricultural fungicide such as, for example,dithiocarbamate and derivatives such as ferbam, ziram, maneb (manganeseethylenebisdithio-carbamate), mancozeb, zineb (zincethylenebisdithiocarbamate), propineb, metham, thiram, the complex ofzineb and polyethylene thiuram disulfide, dazomet, and mixtures of thesewith copper salts; nitrophenol derivatives such as dinocap, binapacryland 2-sec-butyl-4,6-dinitrophenyl isopropyl carbonate; heterocyclicstructures such as captan folpet, glyodine, dithianon, thioquinox,benomyl, thiabendazole, vinolozolin, iprodione, procymidone,triadimenol, triadimefon, bitertanol, fluoroimide, triarimol,cycloheximide, ethirimol, dodemorph, dimethomorph, thifluzamide andquinomethionate; miscellaneous halogenated fungicides such as:chloranil, dichlone, chloroneb, tricamba, dichloran andpolychloronitrobenzenes; fungicidal antibiotics such as: griseofulvin,kasugamycin and streptomycin; miscellaneous fungicides such as diphenylsulfone, dodine, methoxyl, 1-thiocyano-2,4-dinitrobenzene,1-phenyl-thiosemicarbazide, thiophanate-methyl and cymoxanil;acylalanines such as furalaxyl, cyprofuram, ofurace, benalaxyl, andoxadixyl; fluazinam, flumetover, phenylbenzamide derivatives such asthose disclosed in EP 578,586-A, amino acid derivatives such as valinederivatives disclosed in EP 550,788-A, methoxyacrylates such as methyl(E)-2-(2-(6-(2-cyanophenoxy)pyrimidin-4-yloxy)phenyl)-3-methoxyacrylate,benzo(1,2,3)thiadia-zole-7-carbothioic acid S-methyl ester, propamocarb,imazalil, carbendazim, myclobutanil, fenbu-conazole, tridemorph,pyrazophos, fenarimol, fenpiclonil, pyrimethanil, and combinationscomprising one or more of the foregoing fungicides.

In addition to biocide preservatives, it may be desirable to treatgypsum products with fire retarding chemicals such as borax/boric acid,guanylurea phosphate-boric acid, dicyandiamide phosphoric acidformaldehyde, diethyl-N,N-bis(2-hydroxyethyl)-aminomethyl phosphate, andcombinations comprising one or more of the foregoing additives. Thesefire retardants are readily incorporated into nanoparticles formed, forexample, from polyvinylpyridine or polyvinylchloride. Other additivesthat are confer desirable characteristics and which may be added to thecompositions include water repellants, colorants, UV inhibitors,adhesive catalysts, and combinations comprising one or more of theforegoing additives.

While certain embodiments and best mode of the present invention aredescribed herein, these embodiments are merely illustrative. It will beapparent to those skilled in the art that modifications may be madetherein without departing from the spirit of the invention and the scopeof the appended claims.

1. A method for making a gypsum product, comprising: forming a slurryfrom gypsum, water and an emulsion comprising a wax component comprisinga nonsaponifiable wax and a saponified wax, an alkyl phenol component, adispersant/surfactant, a carboxymethylcellulose component, and water;and forming the slurry into a solid product.
 2. The method of claim 1wherein the wax component comprises about 25% to about 50% of theemulsion, by weight.
 3. The method of claim 1 wherein the wax componentcomprises about 30% to about 40% of the emulsion, by weight.
 4. Themethod of claim 1 wherein the nonsaponifiable wax is a slack wax, ascale wax, a paraffin wax or a combination thereof.
 5. The method ofclaim 1 wherein the saponified wax is produced by reaction of asaponifiable wax with ammonium hydroxide, an alkali metal hydroxide or acombination thereof.
 6. The method of claim 5 comprising a saponifiedwax produced by reaction of a saponifiable wax with potassium hydroxideor sodium hydroxide.
 7. The method of claim 5 comprising a saponifiedwax produced by reaction of a saponifiable wax with ammonium hydroxide.8. The method of claim 1 wherein the alkyl phenol component comprises aC₂₀-C₄₂ alkyl group.
 9. The method of claim 1 wherein the alkyl phenolcomponent comprises a C₂₄-C₃₄ alkyl group.
 10. The method of claim 1wherein the alkyl phenol component comprises a C₂₄-C₂₈ alkyl group. 11.The method of claim 1 wherein the dispersant/surfactant comprises apolynaphthalenesulfonic salt.
 12. The method of claim 1 wherein thealkyl phenol component comprises an alkyl phenol having an alkyl groupthat has an average carbon chain length that matches the carbon chainlength of the carboxymethylcellulose.
 13. The method of claim 1, whereinthe nonsaponifiable wax comprises about 33% to about 35% of theemulsion, by weight; the saponified wax comprises about 3% to about 5%of the emulsion, by weight; the alkyl phenol component comprises about0.5% to about 2.5% of the emulsion, by weight; the dispersant/surfactantcomprises about 0.5% to about 2% of the emulsion, by weight; and thecarboxymethylcellulose component comprises about 0.2% to about 5% of theemulsion, by weight.
 14. The method of claim 13 wherein the saponifiedwax is produced by a reaction of a saponifiable wax with ammoniumhydroxide, and further comprising about 0.5% formaldehyde, by weight.15. The method of claim 1 wherein the gypsum product comprises gypsumboard.
 16. The method of claim 1 wherein the slurry further comprisesabout 50 wt. % to about 95 wt. % of a lignocellulosic material based onthe combined weight of the lignocellulosic material and gypsum.
 17. Themethod of claim 13 wherein the gypsum product comprises gypsum board.18. The method of claim 13 wherein the slurry further comprising about50 wt. % to about 95 wt. % of a lignocellulosic material, by thecombined weight of the lignocellulosic material and the gypsum.
 19. Themethod of claim 13 wherein the gypsum product comprises a gypsum woodfiber product.
 20. The method of claim 1 wherein the emulsion containswax in an amount of about 1.5 wt. % to about 3 wt. % by weight of thefinished product.
 21. The method of claim 13 wherein the emulsioncontains wax in an amount of about 1 wt. % to about 3 wt. % by weight ofthe finished product.
 22. The method of claim 1 wherein the slurrycomprises a preservative in an amount of about 0.0025 wt. % to about 0.2wt. % by weight of the product.
 23. The method of claim 13 wherein theemulsion comprises about 0.1% to about 2% preservative, by weight.